Spatial audio processing involves the localization of a sound object (a sound source) in a three dimensional space.
For a person wearing headphones a sound object may be located at a three dimension position (e.g. at (r, ϑ, Φ) in spherical co-ordinates) by providing an appropriate input signal xL(t) to a left ear loudspeaker and an appropriate input signal xR(t) to a right ear loudspeaker.
The input signal xL(t) is produced by processing the audio signal x(t) using a first head related transfer HRTF (r′, ϑ′, Φ′, L) for the left ear.
The input signal xR(t) is produced by processing the audio signal x(t) using a second head related transfer HRTF (r′, ϑ′, Φ′, R) for the right ear.
The location of the sound object in a frame of reference of the sound space (r, ϑ, Φ) is mapped into a location of the sound object in a listener's frame of reference (r′, ϑ′, Φ′). The orientation of the listener's frame of reference is determined by the orientation of the listener's head. This allows a sound source to be correctly placed in the sound space while the listener moves his head.